The present invention relates to an improved rotation angle sensor, and more particularly relates to a novel rotation angle sensor utilizing a photoelectric system containing, as a principal components, a sensor disc of a specially designed optical transmittancy distribution for easy and accurate detection of rotation angle of a body.
In order to know whether or not a certain body is advancing correctly in the originally purposed direction and what is the degree of deviation in advancing direction of the body from the standard direction, it is necessary to detect the rotation angle of the body from the original direction or the standard direction. A typical example of such a rotation angle system is the well known gyrocompass which utilizes the earth magnetism and takes the north-south direction as the above-described standard direction. There is another type of the rotation angle detection which is carried out on the basis of change in the optical quantity transmitting through a light permeable panel, the change being caused by rotation of the panel about a selected rotation axis.
One example of the conventional rotation angle detecting system utilizes a pair of polarizer panels used in combination with each other. The pair of polarizer panels are arranged in spaced relationship with each other in the direction of the rotation axis. One of the polarizer panels is arranged immovably and the other is arranged rotatably about the rotation axis. Rotation of one polarizer panel relative to the other polarizer panel causes a change in the optical quantity transmitting through the two polarizer panels. Thus, the magnitude of the above-described change in the transmitting optical quantity detects the rotation angle of a given body, which is fixed to the other polarizer panel.
Now, taking the disposition as the 0 degree rotation angle, i.e. the standard direction, in which the transmitting optical quantity shows the middle value, the transmitting optical quantity reverses at the rotation angle of .+-.45 degrees from the standard direction. In other words, in the case of the conventional rotation angle detecting system utilizing the pair of polarizer panels, it is quite impossible to detect change in the direction exceeding .+-.45 degrees from the standard direction, which is very inconvenient for practical uses.